1. Field
The embodiments described below relate to systems to control radiation field shape and/or dose distributions within a radiation field.
2. Description
X-ray imaging is used to acquire images of internal patient volumes. Generally, an x-ray image is formed by emitting x-rays toward a patient volume and detecting the x-rays over an area after they have passed though the patient volume. Intensities of the detected x-rays are converted to pixel intensities over the area. The pixel intensities therefore comprise an image in which materials having different attenuative properties are represented by different pixel intensities. As a result, the image illustrates internal structures through which the x-rays have passed.
In order to minimize the exposure of the patient to x-ray radiation, an imaging plan is typically designed to primarily deliver radiation to a region of interest. The imaging plan specifies an angle at which the x-rays are to be delivered to the patient, as well as a shape of the delivered radiation field. The angle is controlled by rotating an x-ray tube around the patient, and the shape is controlled using a collimator.
A conventional collimator is disposed between the x-ray tube and the patient, and includes two pairs of “jaws” disposed perpendicularly to one another. Each jaw is composed of a set of radiation-blocking “leaves”, each of which may be moved linearly into and out of a radiation field emitted by the x-ray tube. The leaves may therefore be controlled to define a rough outer perimeter of a radiation field delivered to the patient.
Known imaging systems may employ electrophysiological signals (e.g., an electrocardiogram (ECG) signal, a blood pressure signal, and/or a respiration signal) to trigger x-ray emission and image acquisition. Such triggering may reduce the influence of patient movement (external and internal) on the acquired images. For example, a conventional system may acquire images at uniform time intervals during a specified signal portion (e.g., Q-wave, S-wave, etc.).
Improved control over radiation field shape and radiation dose is desired.